The demand for cleaner transportation fuels is becoming greater every year. For example, there is great pressure in the United States, as well as in the European Community, for an ever cleaner gasoline pool. The gasoline pool is typically derived from several refinery processes, including gasoline from the catalytic cracking unit, straight run naphtha, reformate, and gasoline obtained as a low boiling by-product from various other refinery operations. Two of the major sources of gasoline are the reformer, in the form of a reformate, and the catalytic cracker, in the form of a heavy catalytic naphtha also referred to as heavy cat naphtha. Both sources present a problem meeting the terms of ever stricter environmental regulations. For example, reformate typically contains unacceptably high levels of benzene, and heavy catalytic naphtha typically contains unacceptably high levels of C.sub.10 + aromatics.
Benzene is produced in a reformer by the dehydrogenation of C.sub.6 cycloparaffins, the dehydrocyclization of straight chain paraffins of appropriate chain length (C.sub.6), and dealkylation of other aromatics. In fact, most reforming units built in recent years are continuous catalytic reforming units which produce ever higher levels of benzene then do reforming units such as semi-regenerative and cyclic units.
While it is possible to remove benzene from the gasoline pool by fractionation techniques, such techniques are not preferred because the boiling point of benzene is too close to that of some of the more desirable organic components, C.sub.6 paraffins and isoparaffins. Toluene and xylenes, are the more desirable organic components, as opposed to benzene, in gasoline because they are less objectionable from an environmental point of view.
Therefore, there is still a significant need in the art for methods of reducing the levels of benzene and C.sub.10 + aromatics from refinery streams destined for the gasoline pool.